In the information and electronics industries, demands for new materials showing higher functionality with elements of smaller size is increasing over inorganic materials such as silicon oxide and silicon nitride which have been generally used so far.
As a material capable of satisfying the requirement of higher functionality, polymers have been drawing great interests due to their excellent properties including low dielectric constant and moisture absorption, excellent adhesion to metal, strength, thermal stability and transparency, and a high glass transition temperature (Tg>250° C.).
The polymers having above-mentioned properties can be used as insulating films of semiconductor or TFT-LCD, protective films of polarizing plates, and electronic components such as multichip modules, integrated circuit (IC), printed circuit board, encapsulants for electronic materials, and flat panel displays.
Cyclic olefin-based polymers which are composed of cyclic monomers such as norbornenes exhibit much better properties than conventional olefin-based polymers, showing higher transparency, better heat and chemical resistance, and lower bi-refringence and moisture absorption. Thus, they can be used for various applications, e.g., optical components such as CDs, DVDs and POFs (plastic optical fibers), information and electronic components such as capacitor films and low-dielectrics, and medical components such as low-absorbent syringes, blister packaging, etc.
Since cyclic olefin-based polymers can be used in such various applications, many studies have been extensively conducted on their commercial applications in academic and industrial fields.
The preparation methods of catalysts with high activity have been mostly studied, but there have been comparatively few studies on the polymerization and post-treatment process that is advantageous in commercial scale from an economic viewpoint.
Until now, a solution polymerization method has been generally used to prepare cyclic olefin-based polymers. The solution polymerization is typically performed by mixing catalyst and monomer in a solvent such as toluene at a predetermined temperature, thus both of monomer and synthesized polymer are dissolved in the solvent and maintained as a single liquid phase during the entire reaction time.
As the conversion increases, the concentration of the polymer in the solution is gradually increased, and the viscosity of the solution is thereby increased. From the initial stage of the reaction to the end, phase separation or phase conversion does not occur during the reaction, and the polymerization reaction is completed in a single homogeneous liquid phase. In other words, when the polymerization is completed or even during the reaction the polymers obtained by the polymerization are completely dissolved in the solvent.
After the polymerization is completed, a dropwise addition method using an antisolvent such as alcohol (methanol, ethanol, etc.), hexane, and cyclohexane is performed in order to precipitate and recover the polymers dissolved in the solvent.
Antisolvent means an organic liquid solvent that is miscible with the solvent of polymer solution but does not dissolve the desired cyclic olefin-based polymer to be separated.
As for the dropwise addition method, there is a method of slowly adding the antisolvent dropwise to the polymerization solution and a method of slowly adding the polymerization solution dropwise to the antisolvent (reverse).
The cyclic olefin-based polymers can be prepared using any one of the methods, which is selected by considering the properties of the polymer and polymerization solution, and properties of the formed particles.
In this step, the kind of antisolvent to be used is also important in the precipitation by the dropwise addition.
Examples of the antisolvent generally used include at least one alcohol-based solvent selected from methanol and ethanol, at least one nonpolar solvent selected from normal hexane, cyclohexane and heptane, and acetone-based solvents.
However, in the precipitation process by the dropwise addition, an excessive amount of antisolvent, typically 5 times to 20 times more than the pure polymer, should be used in order to completely precipitate the polymers dissolved in the polymerization solution in solid particles form.
If a commercial process for a large scale production is concerned for this polymer recovery method of dropwise addition of antisolvent, the excessive amount of antisolvent used for polymer recovery has to be reused. This means that in order to recover and purify the used antisolvent, fractional distillation has to be performed using multiple distillation columns, which requires high costs for equipment and operation.
Further, after precipitating the polymers by the dropwise addition method, post-treatment process including separation of the polymer from the antisolvent and washing/drying of the polymer should be followed.
Generally, the polymer needs to be desirably recovered in a particle or pellet form for packaging. However, the cyclic olefin-based polymer does not melt at a typical extrusion temperature of 200 to 300° C. The polymer will be decomposed by further increase of temperature. Also, the cyclic olefin-based monomers typically show extremely high boiling point temperature (>150° C.), making it difficult to recover polymer through conventional steam stripping process.
Accordingly, due to the above-mentioned thermal properties of the cyclic olefin-based monomers and polymers, it is impossible to obtain the pellet form of polymer using extruder-type equipment.
The preparation method of the cyclic olefin-based polymers using conventional solution polymerization method is advantageous with respect to polymerization yield, molecular weight of the obtained polymer, and amount of the used catalyst. However, it has a significant disadvantage in that a high cost is required to recover the polymer in a particle form from the obtained polymer solution when the polymer is not melt-processable and its monomers have high boiling point temperature.